A LCD display is not a light generator, but rather a light controller. That light can come from the front of the device and be reflected by a mirror at the back; this is the common application for calculators and watches. They can also get the light from a light source at the back (in place of the mirror and frequently LED's) and then control the light that shines out thru the front. This is the method used for computer monitors and TV's. The basic principle is to have two polarizing filters at some specific angle, such as 45° to 125°, and more preferably 60° to 110°, and most preferably from 80° to 100°. The heart of the device is the liquid crystal layer working as a waveguide to change the polarization of the light. If this remains the case, no light will get thru and the display will be dark, and preferably black (indicating that light in the visible wave range is not transmitted through the display). There are a number of types of liquid crystal and which include, for example, nematic, cholesteric, dichroic, discotic and blue phase liquid crystals, all of which may have advantageous application in the present invention. When a voltage is applied to the liquid crystal layer the organic molecules adjacent to the electrode twist the light polarization allowing it to pass thru to the second polarizing filter for the transmissive LCDs or be reflected back by the mirror and allow the light to pass thru for the reflective LCDs. The invention is also useful in OLED displays. In these organic light-emitting diode (OLED) the display includes a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound (rather than the liquid crystal types mentioned above) which emits light in response to an electric current. This layer of organic semiconductor is situated between two electrodes; typically, at least one of these electrodes is transparent, and is advantageously the TCO in accordance with the present invention.
The voltage that is applied to the liquid crystal layer is applied thru a TCO. (i.e., a positive electrode) The criteria of good TCO layer are light transmittance—i.e. above 80%, and preferably above 85%, and more preferably above 87% in the visible wavelength—and low sheet resistance i.e. <100, and preferable less than 80 and most preferably less than <50Ω/□. In most applications, voltage is applied on one side thru a pattern that will determine which portion of the liquid crystal will change polarization. The TCO on the other side (called the negative electrode in the picture) completes the circuit. This is not necessarily patterned. For TV's and monitors the pattern becomes a matrix of pixels, and for color LCD's there are red, green and blue sub-pixels with a color mask for each.